Specimen chamber for electron microscopes



July 1 1947.

F. E. RUNGE ETAL SPECIMEN CHAMBER FOR ELECTRON MIC ROSCOPES Filed April 19, 1944 3 sheets-sheet 1 INVENTOIE July 1947- F. E. RUNGE ETAL SPECIMEN CHAMBER FOR ELECTRON MICROSCOPES 3 Sheets-Sheet 2 Filed April 19, 1944 IJg EN TORE 629mm July 1, 1947.

F. E. RUNGE ETAL 42,423,158

SPECIMEN CHAMBER FOR ELECTRON MICROSCOPES Filed April -19, 1944 3 Sheets-Sheet 3 IN V EN TOR5.

197' TOE/Vi) Patented Juiy 1, 1947 SPECIMEN CHAIVIBER FOR ELECTRON MICROSCOPES Frank E. Runge, Haddon Heights, and Perry C. Smith, Moorestown, N. J., assignors to Radio Corporation of America, a corporation of Deiaware Application April 19, 1944, Serial No. 531,748

10 Claims. 1

The present invention relates to electron microscopes and more particularly to the specimen chamber assembly.

Some of the objects of the present invention are: to provide an improved specimen chamber having ready accessibility as a feature; to provide a novel mounting for the stage on which the specimen holder is mounted; to provide means for transmitting mechanical motion to the interior of the specimen chamber in a leakproof manner; to provide a rugged but sensitive mounting for the stage of a specimen holder; to provide means for damping vibrations of the stage of a specimen holder caused by building or other disturbing vibrations; to provide an adjustment for the stage of a specimen holder wherein one adjustment is linear and the other is arcuate to thereby prevent spurious and uncontrollable stage motions; to provide a novel leak-proof closure for the access-hole of a specimen chambar; to provide a novel specimen holder so ar-- ranged as to change the position of the specimen with respect to the electron stream to produce two images capable of observation for stereoscopic efiect; to provide means exterior of the evacuated column for tilting the specimen holder from one position to another while maintaining the evacuated condition; and to provide other improvements as will hereinafter appear.

In the accompanying drawings, Fig. 1 represents a vertical axial section of a portion of the column of an electron microscope, said section including the specimen chamber and embodying one form of the present invention; Fig. 2 represents a section on line HII of Fig. 1 Fig. 3 represents a detail in elevation of the remote control adjusting means; Fig 4 represents a detail in section on line IV-IV of Fig. 2; Fig. 5 represents a section on line VV of Fig. 1; Fig. 6 represents a detail in plan of the movable stage for adjusting the position of the specimen holder; Fig. '7 represents an elevation of the inner end of the closure shown in Fig. 1; Fig. 8 represents a sectional detail on line VIIL-VIII of Fig. 6; Fig. 9 represents an exploded perspective of the specimen holder and associated parts; Fig. 10 represents a section on line XX of Fig. 1 with the holder shown in neutral position; Fig, 11 represents a section similar to 10 but showing the holder in a tilted position; Fig. 12 represents a section on line IHI-lfllof Fig. 2 and Fig. 13 represents a plan of one -form .of tool for removing parts from the column.

Referring to the drawings, one form of the present invention is shown as assembled i th specimen chamber IQ of the column of an electron microscope such as shown in Frank E. Runges co-pending application Serial No. 530,584, filed April 12, 1944. This chamber I0 is formed in a section H of the column, which latter is suitably secured to the upper and loweradjafient sections of the column to form leakeproof joints. The upper End of the section is formed with an opening 12 of different diameters for receiving parts not here necessary .to illustrate or describe, while the lower end of the section is formed with an opening 13 to accommodate the laterally adjustable annular stage 14. The openings 12 and 13 are axially in register and form portions of the evacuated channel of the microscope. The section -.H is arranged to seat on the next lower section of the column, which in this instance, is the frame 15 of the objective len of the microscope. A groove 16 is provided in the lower face of the section II, encircling the opening 1.4 to receive a packing gasket 1-! for sealing the joint between the parts.

For gaining access to the specimen chamber In, one side of the section H is provided with an access-hole l8, having an annular seat 20 to receive a gasket =2| for sealing purposes. A closure in the form of a plug 22 is arranged to fit snugly against the gasket 2| and seal the access-hole [8 by atmospheric pressure when the chamber 1.0 is evacuated. A handle 23 preferably forms an outwardly projecting part of the plug 2i! for convenient removal or replacement thereof.

For supporting the stage 44 for movement transversely with respect to the axisof the column thereby to ensure accurate alignment of the spec iment holder 24, a plurality of ball-retainingoups 25 are mounted in arcuate shaped relation on the lower face of the stage 14, and each containing a bearing ball 28, arranged to ride respectively upon hardened inserts 2-! set into the upper face of the adjacent frame -l '5.

In order that the stage It can be laterally .a d justed, there are two pairs of posts 29 and 30, preferably formed integral with the stage 44 and rising from e upp r face thereof in relatively close proximity to the inner wall of the chamber to the inner side of a flat strip biasing spring 34. Thus, in the present instance, there are four of the springs 34, respectively adjacent the posts 28 and 30, each being suspended from the top of the chamber at the proper place by fastening screws 35. One spring 33 of each spring pair serves as a biasing abutment opposed to the thrust imparted by its diametrically opposite stage adjusting rod 36. The two rods 36 are arranged respectively to contact optically fiat, hard steel plates 31 on the opposite side of each of two of the springs 34 from the plates 33. In thi instance, the plate 33 juxtaposed to one of the posts 29, is provided with a conical notch 38 to seat the conical end of a pivot pin 39, which projects from the post 29 instead of a ball as in the opposite post 29. Thus, a positive interlock is had between the stage (4 and the biasing spring which nullifies any spurious and uncontrollable stage motions. Thus, while the pin interlock provides a pivotal movement of the stage when the laterally acting adjusting rod is actuated, this arcuate movement is so infinitesimally small that the magnified movement of the specimen holder appears nearly linear.

For mounting the two adjusting rods 36 for axial movement, while maintaining a leak-proof relation of the parts, each passes through a stuffing box and has an extension shank 40, a portion of which is in threaded engagement with a cap sleeve 4| attached to the section I I. Each stufilng box is of novel construction in that a packing 42 is used, formed of oil-pervious rubber held compressed by a coil spring 43, which encircles the rod 36 and is compressed between a follower 44 and the sleeve 4|. A plug controlled port 45 provides a means for introducing oil into the stuffing box to maintain the packing 42 in operative condition. The exterior projecting end of the shank 40 carries a gear 46 arranged for remote control by a flexible shaft leading to the control panel of the instrument for convenient operation. A stop 41 is carried by the gear 46 to limit the arc of travel of the gear. A spring 48 is coiled about the hub of the gear 46 with on end fast to the gear and the other end attached to an adjacent fixed part whereby back-lash of the geared parts is prevented.

From the foregoing it will be apparent that the stage M has a very sensitive adjustment by reason of the ball mountings, and can be accurately shifted for proper alignment of the specimen holder 24 by causing one or the other of the remote controlled gears 46 to be actuated to advance or back-off the rod 36 according to requirements. When advanced the contacted flat spring 34 is flexed inward against the adjacent ball 32 thereby to shift the stage l4 laterally and thus flex the opposite abutment spring 34, so that when the adjusted position is reached the stage I4 is gripped between the pairs of springs, vibration is substantially damped and spurious movements are minimized. When a rod 36 is backedoff the biasing spring pressure causes the stage 14 to follow the movement of the rod 36 operated.

For the purpose of maintaining the plana relation of the stage l4 and further to damp undesired vibrations and to minimize undesired movements, a hold-down means is provided comprising a fixed post 50 upstanding from the objective frame 15, and passing through a hol in the top of the stage l4. Attached to the protruding end of the stud 50 is a strip spring 52 having an arcuate contact 53, preferably of bronze, which seats underthe spring pressure upon the flat, polished hardened head of a stud 54. This stud 54 is fixed in the top of the stage 14. There are preferably several of these hold-down means appropriately located about the stage 14, so that the stage is not only damped against axial vibration but is also held in substantially horizontal position.

Since the closure plug 22 is seated by atmospheric pressure, it can be quickly removed as soon as the vacuum is broken in the column. This removal permits access through the access-hole l8 to the specimen chamber 15 for removal of the specimen holder 24.

While any standard type of specimen holder can be used With the assembly as heretofore described, it is preferred to employ a novel holder which in addition to functioning in the standard way can also be tilted to obtain stereoscopic effects. As here shown, the holder comprises an elongated tubular body 55 arranged at its lower end to mount the apertured cap 55 in which the specimen-supporting screen 51 is carried. The

bore 58 of the body 55 is downwardly converging in the manner of any standard holder.

For supporting the holder, the upper end thereof is clamped between the split portions of a clamp member 68 by means of a screw El, This member 63 seats upon the head flange 62 of a sleeve 63 through which the holder body 55 passes with an encircling clearance between the parts. The flange 82 seats upon the stage 14 while the sleeve 53 and the associate holder body 55 pass through the axial hole 64 in the stage 14. The sleeve 63 i provided with a vertical slot 65 in one side to receive a key 65 projecting from the stage I 4 thereby to prevent rotary turning of the sleeve with respect to the stage.

As a means for tilting the specimen body 55. the upper face of the flange 62 is a convex portion of a cylinder having the specimen as a center, and the lower end of the sleeve is formed on a concave are having the specimen as a center. This latter face is arranged in contact with the upper face of a head 61 having the same spherical curvature in order to ride on the concave end of the sleeve to tilt the body 55 about the specimen as a center. This tilting action held linearly by means of a linear groove 68 in the flange 62, and an interfitting lip 16 on the clamp member 60. Thus, the mounting for the specimen holder contemplates three positions, namely a neutral or normal to the electron optical axis, and one tilted position to either side of the neutral position. Since the angle of tilt is generally about four degrees in either direction, the flange 52 is provided with three equally spaced notche H of which the middle one indicates the neutral position and each of the others one four degree tilt of the holder. A spring pressed ball 12 is carried by a socket type stud l3 threaded into the member for registration with the notches and hence the holder is not only releasably anchored by the ball dropping into a notch but the click of the ball entering a notch can be identified with any selected notch.

In order to tilt the specimen holder while maintaining the vacuum in the specimen chamber, the stud 13, in the present instance, is used and is straddled by two fingers 14 which project from one end of a yoke I5 having at the opposite end two extension arms 16 which respectively enter slots 1'! in the closure plug 22 and are pivoted therein on pins 18 threaded into the plug. Rocking motion is transmitted to the yoke 15 by a circular disc '19 having a diameter equal to the distance between the sides of the yoke and eccentricall'y keyed to a shaft 80 which extends axially through the plug 22, to terminate, exterior of the specimen chamber, in an operating hand knob 8 1. Thus, turning of the knob clockwise or countar-clockwise causes the disc 19 to have a cam action against the yoke sides which shifts the fingers 14 in the direction correspondin to the direction of rotation of the knob 8|, and hence transmits a linear movement to the stud l3 and consequent lateral swing of the specimen holder. As a result, the specimen screen has the required minute angular change whereby the specimen is viewed from an angle to the axis of the evacuated column. For setting the knob Bl in neutral position after having moved the specimen holder to a denied position, the knob has a spring pressed indent plunger 82 projecting from the plug extension to ride in a slot 83 in the knob 81. The ends of this slot 83 form limit stops to the turning of the knob while at the center of the slot there is a groove 84 denoting the neutral position of the yoke. When the indent plunger 82 seats in the groove 84, the observer knows the yoke is in its neutral position, and cannot therefore be in contact with 13 of the specimen holder and therefore cannot interfere with the free movement of the stage.

As a means for preventing leakage along the shaft 80, the plug 22 has a tubular extension 85 forming with a packing 8B, follower 8'! and compression spring 88, a stufiing box which seals the joint between the shaft 80 and the plug 22. The packing 86 is of special oil-pervious rubber particularly efiicient as a. joint sealing means.

In order to expedite the removal of the specimen holder or other parts from the chamber IE3, a lifting tool 90, such as shown in Fig. 13 may be employed.

From the foregoing it will be seen that mechanical motion can be transmitted to the interior of the specimen chamber while under evacu 'ation without leakage to thereby allow, in one instance, the required lateral adjustment of the stage, and, in the other instance, the tiltin of the specimen holder for steroscopic purposes. Furthermore, by the novel specimen holder, a neutral position thereof makes it usable as a standard holder, while a swing to either side of the central axis can be obtained at will without breaking the vacuum or disassembling any parts. A swing of four degrees either side of the axis has been found to give satisfactory results but the invention is not to be considered as limited to this particular arc. Where only standard Work is to be done, namely that requiring no tilting of the specimen holder, the control closure plug may be replaced with a plain plug, that is one without the adjusting means for tilting the specimen holder. In that case also the tilting specimen holder can be replaced with a standard fixed holder, if desired.

What is claimed is:

1. In an electron miscroscope, a member forming a specimen chamber and a portion of an evacuated column, a stage in said chamber for supporting a specimen holder, means to mount said stage for movement transversely of said column, a plurality of upstanding posts carried by said stage, biasing springs attached to said member and respectively juxtaposed to said posts for reaction thereby, two rods extending from the exterior of said member for respectively actuating two of said springs, and means exterior of said member for linear operation of said rods, whereby said stage is adjustable in two directions and vibration thereof prevented.

2. In an electron microscope, a member forming a specimen chamber and a portion of an evacuated column, a stage in said chamber for supporting a specimen holder, means to mount said stage for movement transversely of said column, a plurality of upstanding posts carried by said stage, biasing springs attached to said member and juxtaposed to said posts for reaction thereby, two rods extending from the exterior of said member for respectively actuating two of said springs, polished hardened plates respectively between said rods and the two springs, and means exterior of said member for linear operation of said rods, whereby said stage is adjustable in two directions and vibration thereof prevented.

3. In an electron microscope, a member forming specimen chamber and a portion of an evacuated column, a stage in said chamber for supporting specimen holder, means to mount said stage for movement transversely of said column, four upstanding posts carried by said member and arranged in diametrically opposite pairs, a flat strip biasing spring attached to said member having its free end opposite one of said posts, said end having a notch therein, a pivot projecting from said post to seat in said notch as a pivotal point, bearing balls respectively mounted in the remaining posts, biasing springs attached to said member and juxtaposed respectively to the bearing balls in said remaining posts for reaction thereby, two rods extending from the ex terior of said member and respectively juxtaposed to the ball opposite said pivotal point and to one of the other balls, whereby spurious movement of said stage is prevented, and means exterior or member for linear operation of said rods.

4. In an electron microscope, a member forming a specimen chamber and a portion of an evacuated column, a stage in said chamber for supporting a specimen holder, means to mount said stage for movement transversely of said column, four upstanding posts carried by said member and arranged in diametrically opposite pairs, fiat strip biasing spring attached to said memher having its free end opposite one of said posts, said end having a notch therein, a pivot p50- jetting from said post to seat in said notch as pivotal point, bearing balls respectively mounted in the remaining posts, biasing springs attached to said member and juxtaposed respectively to the bearing balls in said remaining posts for reaction thereby, two rods extending from the exterior of said member and respectively juxtaposed to the ball opposite said pivotal point and to one of the other balls, whereby spurious movement of said stage is prevented, means exterior of said member for linear operation of said rods, and optically polished hardened plates respectively between said balls and springs.

5. In an electron microscope, a member forming a specimen chamber and a portion of an evacuated column, a stage in said chamber for supporting a specimen holder, means to mount said stage for movement transversely of said column, four upstanding posts carried by said member and arranged in diametrically opposite pairs, a flat strip biasing spring attached to said memher having its free end opposite one of said posts, said end having a notch therein, a. pivot projecting from said post to seat in said notch as a pivotal point, bearing balls respectively mounted in the remaining posts, biasing springs attached to said member and juxtaposed respectively to the bearing balls in said remaining posts for reaction thereby, two rods extending from the exterior of said member and respectively juxtaposed to the ball opposite said pivot-a1 point and to one of the other balls, whereby spurious movement of said stage is prevented, means exterior of said member for linear operation of said rods, and optically polished hardened plates respectively between said rods and said springs.

6. In an electron microscope, a member forming a specimen chamber and a portion or an evacuated column and having an access-hole leading to said chamber, a closure plug for said access-hole having an area greater than the trans verse area of said access-hole, the outer face of said plug being exposed to atmospheric pressure and the inner face exposed to less than atmospheric pressure, a stage in said chamber, a specimen holder supported by said stage for tilting movement, and means transversing said plug and operable from the exterior of said chamber for tilting said specimen holder.

7. In an electron microscope, a member form ing a specimen chamber and a portion of an evacuated column and having an access-hole leading to said chamber, a closure plug for said accesshole having an area greater than the transverse area of said access-hole, the outer face of said plug being exposed to atmospheric pressure and the inner face exposed to less than atmospheric pressure, a stage in said chamber, a specimen holder supported by said stage for tilting movement, means traversing said plug and operable from the exterior of said chamber for tilting said specimen holder, and means for sensing the neutral and tilted positions of said specimen holder.

.8. In an electron microscope, a member forming a specimen chamber and a portion of an evacuated column and having an access-hole leading to said chamber, a closure plug for said accesshole having an area greater than the transverse area of said access-hole, the outer face of said plug being exposed to atmospheric pressure and the inner face exposed to less than atmospheric pressure, a stage in said chamber, a specimen holder supported by said stage for tilting movement, means traversing said plug and operable from the exterior of said chamber for tilting said specimen holder, and means including notches and a spring pressed detent for sensing 50 the neutral and tilted positions of said specimen holder.

9. A specimen-holding unit for use in electron microscopes comprising a sleeve having a flange at one end for seating on the stage of the microscope and having a spherical surface at the other end, a specimen holder axially disposed in said sleeve with a clearance thereabout and means including an arcuate surface for supporting said holder on said flange, said holder having a head formed With a spherical surface complemental to and in contact with said sleeve spherical surface, and a screen carried by said head for mounting a specimen, said spherical surfaces and arcuate surface being generated about a point on said screen as a center.

10. A specimen-holding unit for use in electron microscopes comprising a sleeve having a flange at one end for seating on the stage of the microscope and having a spherical surface at the other end, a specimen holder axially disposed in said sleeve with a clearance thereabout and means including an arcuate surface for supporting said holder on said flange, said holder having a head formed with a spherical surface complemental to and in contact with said sleeve spherical surface, a screen carried b said head for mounting a specimen, said spherical surfaces and arcuate surface being generated about a point on said screen as a center, and means to prevent rotation of said sleeve.

FRANK E. RUNGE. PERRY C. SMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,266,717 Von Borries et a1. Dec. 16, 1941 2,277,024 Ruska et al Mar. 17, 1942 2,305,458 Ruska et a1 Dec. 15, 1942 2,268,539 Von Borries et a1. Dec. 30, 1941 2,347,348 Young Apr. 25, 1944 2,272,843 Hillier Feb. 10, 1942 2,360,677 Hillier Oct. 17, 1944 2,220,973 Marton Nov. 12, 1940 2,296,798 Reid Sept. 22, 1942 FOREIGN PATENTS Number Country Date 246,129 Great Britain Jan. 6, 1926 25,530 Great Britain Nov. 26, 1908 11,277 Great Britain May 14, 1913 

